Self-contained imaging media comprising opaque laminated support

ABSTRACT

A self-contained photohardenable imaging assembly comprising in order: a first transparent support; an imaging layer comprising a developer material and a plurality of photohardenable microcapsules encapsulating a color precursor, and a second opaque support, wherein the opaque support comprises a barrier layer that exhibits a low water vapor transmission rate, which barrier layer comprises a metallic material. The imaging assembly has been found to provide better image quality and more consistence sensitometric response to pressure development.

FIELD OF THE INVENTION

The present invention relates to an imaging assembly that comprisesphotohardenable microcapsules containing coloring agents. Development isaccomplished by the application of uniform pressure to the imagingassembly. In particular, the imaging assembly comprises an opaquesupport having a preselected vapor transmission rate in combination withoptical properties that provide for improved image quality andperformance.

BACKGROUND OF THE INVENTION

The present invention relates to an imaging medium in the form of aself-contained imaging assembly and, more particularly, to an improvedself-contained imaging assembly containing a photosensitive imaginglayer or layers comprising photohardenable microcapsules encapsulating acoloring material and, outside the microcapsules, a developer materialdisposed between a first transparent support and a second support whichmay be opaque or transparent. The imaging medium or assembly can also bereferred to as a recording medium, and the imaging layer can be referredto as a recording layer, since the assembly can serve both to capture animage (either the original image or an electronic copy), as does film,and also to display the image, as does a print. Consistent with thisfact, the imaging assembly can form a positive image.

The photosensitive imaging layer (including microcapsules) is colored bypressure development after exposure to radiation based on imageinformation. The microcapsules, whose mechanical strength changes(increases) when exposed to light, are ruptured by means of pressuredevelopment, whereupon the coloring material and other substancesencapsulated in the microcapsules flow out (to varying amounts based onthe exposure) and development occurs. The coloring material, such as asubstantially colorless color former, migrates to, and reacts with, thedeveloper material and coloring occurs, whereupon a color image isdeveloped.

The “rupture” of the microcapsules are not an all-or-nothing event.Rather, the microcapsules exposed to light are differentially photocuredto release varying amounts of color former in order to achieve tonaldepth in the exposed area. The differential exposure to lightproportionately increases the viscosity of the photocurable compositionand thus immobilizes the color former proportionately to the desiredtonal depth in the exposed area. The rupture of the microcapsules andthe release of the color former is accomplished by the uniformapplication of pressure. Development of the photosensitive imaging layercan be accomplished, for example, by passing the imaging assemblybetween a pair of upper and lower nip rollers.

Photohardenable imaging systems employing microencapsulatedphotosensitive compositions are the subject of various patents,including U.S. Pat. Nos. 4,399,209, 4,416,966, 4,440,846, 4,766,050,5,783,353, and 5,916,727. Image forming devices (also referred to asprinters) are disclosed, for example, in U.S. Pat. No. 4,740,809,wherein exposure occurs by guiding a light from a light source for aplurality of colors across a photosensitive recording medium. U.S. Pat.No. 4,992,822 discloses an image forming device, capable of producing aplurality of colors via a polygonal mirror, for repeatedly exposing thesame pixels in a photosensitive recording medium. U.S. Pat. No.5,893,662 discloses a device for printing an image wherein the devicecan be incorporated into a computer bay. U.S. Pat. No. 4,648,699describes a development technique which employs, instead of a pair ofnip rollers, a point contact ball moving relative to the photosensitiverecording medium.

In the most typical embodiments, the photohardenable composition is aphotopolymerizable composition including a polyethylenically unsaturatedcompound and a photoinitiator and is encapsulated together with a colorformer. Exposure to actinic radiation hardens the internal phase of themicrocapsules. Then, as mentioned above, following exposure, the imagingmedia in the form of a sheet can be subjected to a uniform rupturingforce by passing the sheet through the nip between a pair of pressurerollers.

One of the problems in providing a self-contained imaging assembly thatprovides a high quality print is image stability or “keeping” which isaffected by humidity sensitivity. It is known that print quality, and inparticular sensitometric response to actinic radiation, can besignificantly affected by sensitivity to humidity and the relativehumidity of the environment. Even if the media is manufactured andpackaged at a particular humidity, which is found optimum for printquality, variations after the media acclimates to a different laterenvironment can adversely affect the sensitometric properties. This hasbeen believed due to the materials employed in the imaging media, inparticular the degree of hardening or curing of the internal phase of amicrocapsule and the consequent increase in the viscosity varying with achange in humidity. As a result thereof, photographic characteristicssuch as speed, maximum density and fogging density are changed from theoriginal optimum. Furthermore, a full color imaging is adverselyaffected.

In forming a full color image, color precursors which develop intoyellow, magenta and cyan colors and photo-initiators corresponding toblue, green and red lights are encapsulated in an internal phase of themicrocapsules, and the three sets of the microcapsules are mixed toprepare a full color imaging material containing a developer. Thephotographic characteristics of the respective microcapsules vary with achange in humidity to different degrees, resulting in muddy colors orincorrect or suboptimal colors. For example, when it is desired that ayellow color be developed, cyan and magenta capsules are cured by redand green lights, and only a yellow color former reacts with acolor-developer to form an image. However, if the cyan or magentacapsules insufficiently cure due to a change in humidity, the result maybe a muddy color in which cyan or magenta is blended with yellow to someextent. Such muddy colors or other sensitometric phenomena due to achange in humidity has been a significant problem.

One technique that has been used to address the humidity problem and toimprove media stability resides is conditioning the layer containing thedeveloper and microcapsules to a relative humidity (RH) of about 10 to40% and preferably about 20%. For example, U.S. Pat. Nos. 5,916,727 and5,783,353 disclose conditioning the layer at about 20% RH for about 2 to12 hours or more, at ambient temperatures, and subsequently sealing theassembly at this low RH level to assure that the layer is relativelymoisture-free during the normal shelf-life of the assembly.

U.S. Pat. No. 5,996,793 discloses storing the image-forming materialtogether with a humidity-controlling material. Further, the patentdiscloses storing the image-forming material and thehumidity-controlling material within a package made from a low-moisturepermeable film. The low-moisture permeable film can be a plastic film onwhich is deposited a metal. Other low-moisture permeable films mentionedinclude fluorinated resins such as polytetrachloroethylene,polytrifluoroethylene, chlorinated rubber, polyvinylidene chloride, acopolymer of polyvinylidene chloride and acrylonitrile, polyethylene,polypropylene, polyesters, and films obtained by depositing a metal suchas aluminum and a metal oxide such as silicon oxide.

Unfortunately, when the imaging media are not used right away,especially if a plurality of media are stored for some time in aprinting device prior to forming an image, the media may have anopportunity to adjust to ambient humidity and, especially in very dry orvery humid climates, the RH of the media may decrease or increasesubstantially in a short time. Once the imaging media is removed from apackage, it does not take very long for the environmental humidity toaffect the media. Ambient humidity can soon penetrate the outsidesurface support on each side of the media cause a change in the moisturecontent within the media.

U.S. Pat. No. 5,783,353 teaches that commercially available materialsmay be used for the opaque support in media comprising light-sensitive,pressure rupturable microcapsules. Materials listed include paper,cardboard, polyethylene, and polyethylene-coated paper. Opaque films aretypically composites or admixtures of the polymer and the pigment in asingle layer. U.S. Pat. No. 5,783,353 states that, alternatively, anopacifying agent can be provided in a separate layer underlying oroverlying a polymer film such as PET. The patent further states that theopaque support should be sufficiently opaque so that when an imagingmedium is exposed to radiation through the transparent support, theopaque support is effective to prevent the radiation from penetrating toother imaging media which may be stacked behind the imaging mediumduring the exposure step. The patent states, however, that if the unitsare not exposed in a stacked format, the opacity of the support is notcritical so long as the support provides the desired background.

Metal barriers have been used in other contexts, in the photographic andpackaging arts. In the packaging art, excellent oxygen and moisturebarrier properties are desired or required. One approach to improvingthe oxygen and moisture vapor transmission of polymer films in thepackaging art, in particular, is the application of a barrier coating inthe form of a metal coating to the surface of a packaging film, tothereby form a metallized film.

U.S. Pat. No. 6,033,786 teaches a biaxially oriented, heat-set,multilayer film, including a core layer, a bonding layer having asurface adhered to the core layer, and a flame treated surface oppositethe surface adhered to the core layer. A metal coating for providingoxygen and moisture barrier properties is deposited on the flame treatedsurface and a protective plastic film adhered to the metal coating. Thecore layer and bonding layer either are free of void-creating additivesor include only a quantity of such additives that does not create amatte surface adversely affecting the barrier properties of the metalcoating. The bonding layer comprising a mixture including 40 to 100% byweight of propylene/butene-1 copolymer containing up to about 14% byweight of butene-1, 0 to 60% of an isotactic polypropylene, and 0 to 50%of a copolymer of ethylene and propylene wherein propylene is thepredominant component by weight.

Numerous patents disclose various methods of coating a polymer film witha metal. For example, Japanese Pat. Publication No. 61-225049 teachespreparation of metallized polypropylene films by extruding a mixture ofpolypropylene and a hydrocarbon resin and treating the surface thereofwith corona discharge in a nitrogen/CO₂ atmosphere. This treatmentinserts amino and/or amido groups into the surface of the film to adepth of about 100 Angstroms. The thus treated film surface is thenmetallized. U.S. Pat. No. 4,888,237 discloses a metallized film in whichthe surface that is provided with a metallized coating is the surface ofa crystalline polyolefin layer that is flame treated prior to beingmetallized. U.S. Pat. No. 4,487,871, issued to Ishibashi, et al.,discloses a polyolefin resin composition including a propylenebutene-1copolymer having a propylene component in a weight percent of at least70%. This copolymer is present in the range of 96%-80% by weight, andthe composition additionally includes 4% to 20% by weight of a highdensity polyethylene homopolymer or copolymers of ethylene as a maincomponent with other alpha-olefins. U.S. Pat. No. 4,487,871 disclosescorona treating a surface of the composition to be provided with a metalcoating.

After extensive investigation, Applicants have found that humidityaffects the mechanical properties of the imaging layer in aself-contained imaging assembly comprising photohardenablemicrocapsulated coloring agents, as compared to affecting the reactionproperties of materials during photohardening of the imaging layer. Thiseffect on mechanical properties causes undesirable variations in thedegree of rupture of the microcapsules when the media is subjected topressure during development. Although not wishing to be bound by theory,this may be due to the humidity changing the break strength of thecapsules and/or it may be due to the change in pressure applied on thecapsules due to the change in the stiffness of the image layer which inturn increases the stress applied to the microcapsules, more likely thelatter.

An object of the present invention is, therefore, to provide aself-contained photohardenable imaging assembly that is resistant to theaffect of humidity and which will print consistently in response to ameans for applying pressure to the assembly.

Another object of the present invention is to provide a self-containedphotohardenable imaging assembly that provides better image quality byproducing greater whiteness, opacity and reflectance.

Still another object of the present invention is to obtain an improvedmedia that has no significant change in sensitometric properties withrelative humidity, based on speed, Dmax, Dmin, tonal scale, and fullcolor correctness.

Still another object is to obtain an improved media that has improvedRaw Stock Keeping (RSK), from manufacture to use.

It would be particularly desirable if these objectives could beaccomplished without requiring radical changes in conventional imagingchemistry, with respect to the microcapsules and the developer. It wouldbe advantageous if these objectives could be attained in a product thatwas economical to manufacture and inexpensive for the customer topurchase.

SUMMARY OF THE INVENTION

In the self-contained imaging assembly of the present invention, animaging layer containing developer and photohardenable microcapsules isplaced between two support members to form an integral unit, wherein onesupport is transparent and one support is opaque, comprises a metallicbarrier layer, and exhibits a water vapor transmission rate of less than0.77 g/m²/day (0.05 g/100 in²/day). The opaque support also has veryhigh opacity and reflectance at the interface with the imaging layer.Preferably, the imaging assembly is also sealed on the sides to furtherprevent water vapor from permeating out of the imaging layer. The term“sealed,” as used herein, refers to a seal which is designed to benon-temporary. This seal is maintained during printing of the image andin the final imaged product, as compared to a temporary package.

In the imaging assembly of the invention, a first support is transparentand a second support is opaque. Consequently, an image is providedagainst a substantially white background as viewed through thetransparent support. Sometimes herein the first support may be referredto as the “front” support and the second support may be referred to asthe “back” support.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a prior-art imaging system.

FIG. 2 is a cross-sectional view of the prior-art imaging system of FIG.1 after exposure and microcapsule rupture.

FIG. 3 is a cross-sectional view of an imaging system having an opaquesupport according to the present invention.

FIG. 4 is an embodiment of an opaque support according to the presentinvention comprising more layers than the opaque support of FIG. 4.

FIG. 5 shows, based on the results of Example 1 below, the Dmin changefor a barrier treated media for use in the present invention, at 40%relative humidity and 70° F. as a function of time, for a yellow dye.

FIG. 6 shows, based on the results of Example 1 below, the Dmin changefor a barrier treated media for use in the present invention, at 40%relative humidity at 70° F. as a function of time, for a magenta dye.

FIG. 7 shows, based on the results of Example 1, below the Dmin changefor a barrier treated media for use in the present invention, at 40%relative humidity/70° F. as a function of time, for a cyan dye.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a self-contained imaging assemblyfor both developing and printing an image, which assembly providesimproved image quality by reducing the variation in the sensitometricresponse of the media caused by changes in the relative humidity of theenvironment.

By the term “raw stock keeping” (RSK) is meant the stability of theproduct from time of manufacture to time of use by the customer. Anothermetric of concern is “media shelf life” which is defined as thestability of the product from the time of opening a presealed packagecontaining the media to the time of consumption (printing) of the media.Typically, a package may contain a plurality of media, for example 20media.

As mentioned above, the self-contained imaging assembly comprises animaging layer or series of layers in which a color developing material(also referred to as a color developer) reacts with a dye precursor(also referred to as a color former) inside microcapsules. Typically,the microcapsules encapsulate photohardenable compositions comprising aphotosensitive initiator and hardenable material that undergoes a changeof mechanical strength when irradiated with light of a predeterminedwavelength, wherein the plurality of microcapsules encapsulates at leasta dye precursor for coloring when brought into contact with the colordeveloping material.

The plurality of microcapsules comprises three different types ofmicrocapsules. The three types of microcapsules encapsulate thepolymerization initiator, photocurable resin (each photocuring byirradiation with light of one of the three primary colors of light,respectively), and the colorless dye precursors for producing each ofthe colors of yellow, magenta and cyan. For example, when irradiatingthe self-contained imaging assembly with blue light (with a wavelengthof about 470 nm), the photocurable resin of the microcapsules containingonly yellow dye precursors is photocured, and these microcapsules(yellow) differentially rupture even when pressure developing theself-contained imaging assembly; however the microcapsules which werenot photocured (magenta and cyan) rupture and the magenta and cyan dyeprecursors are forced out from the microcapsules and react with thecolor developing material, whereupon coloring occurs, and these colorsmix to become a blue color, whereupon this blue color can be seenthrough the light-transmitting support.

Further, when irradiating the self-contained imaging assembly with greenlight (with a wavelength of about 525 nm), the photocurable resin of themicrocapsules containing only magenta dye precursors is photocured, theyellow and cyan microcapsules are ruptured by pressure development, andas a result of the reaction of the color developing material with theyellow and cyan dye precursors the respective coloring occurs, whereuponthese colors mix to become a green color. Moreover, when irradiating theself-contained imaging assembly with red light (with a wavelength ofabout 650 nm), the photocurable resin of the microcapsules containingonly cyan dye precursors is photocured, the yellow and magentamicrocapsules are ruptured by pressure development, and as a result ofthe reaction of the color developing material with the yellow andmagenta dye precursors the respective coloring occurs, whereupon thesecolors mix to become a red color.

Furthermore, when all microcapsules are photocured to maximum hardnessby exposure to light corresponding to the three types of microcapsulespreviously mentioned, they do not rupture even by pressure development.Therefore coloring does not occur, and the surface of the opaque supportcan be seen through the light-transmitting support, i.e. the surfacecolor (white in the present embodiment) of the opaque support becomesthe background color. In short, a color image is formed only in theareas where a coloring reaction occurred when the microcapsulesruptured. This coloring principal is sometimes called “self-coloring.”

A prior-art image assembly is illustrated in FIG. 1 which imagingassembly 1 comprises in order: a first transparent support 2, a subbinglayer 3, an imaging layer 4 comprising photohardenable microcapsules 5and a developer material 6, a layer of adhesive 8, and a second support10 which may or may not contain an opacifying agent 12. By image-wiseexposing this unit to actinic radiation, the microcapsules aredifferentially hardened in the exposed areas and the exposed unit canthen be subjected to pressure to rupture the microcapsules.

FIG. 2 illustrates the prior-art imaging assembly of FIG. 1 afterexposure and rupture of the microcapsules 5. Ruptured microcapsules 16release a color forming agent, whereupon the developer material 6 reactswith the color forming agent to form an image 14. The image formed isviewed through the transparent support 2 against the support 10 whichcan contain a white pigment. Typically, the microcapsules will consistof three sets of microcapsules sensitive respectively to red, green andblue light and containing cyan, magenta and yellow color formers,respectively, as described above and disclosed in U.S. Pat. No. 4,772,54and U.S. Pat. No. 4,440,846.

Imaging layer 4 typically contains about 20 to 80% (dry weight)developer, about 80 to 20% (dry weight) microcapsules and 0 to 20% of abinder. The layer is typically applied in a dry coat weight of about 8to 50 g/m². An example of such a coating formulation is illustrated inExample 1 of U.S. Pat. No. 5,916,727.

According to the present invention, the second support of the imagingassembly is opaque and is 10 to 250 microns in thickness, comprises ametallic water vapor barrier layer, which may comprise part of ametallized water vapor barrier sheet, and one or more image-backgroundlayers for providing photographic quality whiteness to the formed image.The image-background layers are typically closest to the imaging layerof the imaging assembly in relation to their function of providingwhiteness. The entire support provides a light reflectance (at theinterface with the overlying imaging layer) of greater than 80%,preferably greater than 90%, most preferably greater than 95%. The watervapor transmission rate (WVTR) of the opaque support of the invention isless than about 0.77 g/m²/day (0.05 gm/100 in²/day) and preferably lessthan about 0.15 g/m²/day (0.01 g/100 in²/day) at 38° C. and 100% RH. TheWVTR is measured according to ASTM Test F1249-90, hereby incorporated byreference.

By the term “support,” as used herein, whether referring to thetransparent or the opaque support, is meant the material extending fromthe outside of the assembly to the imaging layer, whether from thebottom or from the top, except not including the adhesive layer that isused to promote adhesion of the support to the adjacent imagingcomposition. At least the opaque support, as indicated above, comprisesat least one water vapor barrier layer and typically is a laminate withother layers that provide opacity, stiffness, and light reflectance.

By the term “barrier layer” or “barrier material” is meant a materialthat has a water vapor transmission rate of less than 0.77 g/m2/day(0.05 g/100 in²/day) by the ASTM F-1249 test. Since the barrier layer isonly a part of the opaque support, the support may have other layersthat provide a higher water vapor transmission than the barrier layer,so long as the water vapor transmission rate of the entire opaquesupport, and preferably both supports, is less than 0.77 g/m2/day (0.05g/100 in²/day). The opaque support comprising a barrier layer may bereferred to as an “opaque barrier support.” A separable part of theopaque barrier support containing a barrier layer may be referred to asa “barrier sheet,” for example, when referring to a materialcommercially available for use in the present invention, which sheet islaminated to another sheet or layer during manufacture.

To evaluate the whiteness of the opaque support below the imaging layer,a HUNTER spectrophotometer CIE system D65 procedure can be employed tomeasure the L Star UVO (ultraviolet filter out). In this test a controlsample consisting of a standard color photographic paper can be used tocompare the results. L Star UVO values of 92.95, for example, areconsidered typical. The opacity of the opaque support can also bemeasured by the HUNTER spectrophotometer CIE system D65. Opacity is ameasure of combined light scattering and absorbing power of a specimen.The HUNTER spectrophotometer has a known light source that istransmitted onto the surface of a sample backed by a white reflectivetile and a black absorbant tile and indicates the diffuseness or hidingpower. A value of 100% would mean that nothing is absorbed and onlyreflected light is measured. The metallized water vapor barrier sheetemployed in the practice of the invention can be a metal foil, a metalcoated plastic film, or an aluminum metallized plastic film. Themetallic barrier layer can comprise at least one material selected fromthe group of aluminum, nickel, steel, gold, zinc, copper, titanium, andmetallic alloys. The metallic layer can be applied by a variety of knowndeposition techniques, for example, vacuum deposition including chemicalvapor deposition, electron beam evaporation, plasma-type sputteringdeposition, ion-assisted deposition such as ion plating, as well asothers well known to those skilled in the art of vacuum coating ordeposition. The preferred material comprises a vacuum deposited layer ofaluminum.

Exemplary metallized water vapor barrier sheets (comprising a metalliclayer) are commercially available, for example, Hicor™ 115 MHD, 35MU842,Bicor™70 MET-HB, and 205MET-TWSB (all from Exxon-Mobil Corp.) andmetallized 200 gauge Melinex™ 453 polyester film, metallized 142 gaugeHOECHST™ polyester film, metallized 92 gauge polyester film, metallized50 gauge “S” polyester film, and metallized 50 gauge Melinex™ 197 PET(all from CPFilms, Inc.). The metallized water vapor barrier sheet maybe a laminate which comprises a combination of two or more metallizedfilms. The water vapor barrier sheet may further comprise one or morepigmented layers to reduce or hide the metallic sheen of the metallizedlayer.

The one or more image-background layers for providing photographicquality whiteness to the formed image can comprise a microvoided polymerfilm, a microvoided polymer film laminated on a plastic or a papersubstrate, a resin coated paper or a pigmented resin coated plasticfilm. In a preferred embodiment, the microvoided polymer film is amicrovoided polyester or polyolefin film. In a particularly preferredembodiment the microvoided polymer film is a biaxially orientedmicrovoided polyester or polyolefin film. Preferably the polyolefin ispolypropylene and the polyester is poly(ethylene terephthalate).Alternately, the light reflective sheet may comprise, for example, apolyethylene terephthalate sheet containing about 10% titanium dioxidewhich provides a bright white support. Such a support is commerciallyavailable from DuPont Co. under the product designation Melinex™.

In one particular embodiment, a metallized water vapor barrier sheet islaminated to a biaxially oriented polymer film on one side and a papersheet on the other side. The metallized water vapor barrier can belaminated to the paper base with the use of a melt adhesive or a solventor aqueous coated adhesive.

The opaque support contains an opacifying agent in the one or moreimage-background layers which may consist of a laminated sheet or aplurality of laminated sheets in front of the barrier sheet. Theopacifying agent employed in the reflective sheet or other layers is aninert, light-reflecting material which exhibits a white opaquebackground. Materials useful as the opacifying agent include inert,light-scattering white pigments such as titanium dioxide, magnesiumcarbonate or barium sulfate. In a preferred embodiment the opacifyingagent is titanium dioxide.

The opaque support at its face side, i.e., the side of the support thatis closest to the imaging composition, has a light reflectance that ispreferably greater than 90 percent and more preferably greater than 95%.It has been found that this is advantageous in improving the quality ofthe image.

In one preferred embodiment of the invention, the opaque second support,10 to 250 microns thick, has a water vapor transmission rate of lessthan 0.77 g/m2/day (0.05 g/100 in²/day) and comprises in order startingfrom the outside of the assembly: a backing layer, an aluminummetallized water vapor barrier sheet; a tie layer, a paper sheet, a tielayer, and a biaxially oriented microvoided polyolefin film or a resincoated pigmented polyolefin film. By the term “tie layer” is meant arelatively thin layer that is used to promote adhesion between thickerlayers, films, or sheets. The water vapor barrier sheet is preferably asimple metallized polyester or polyolefin film or a metallized compositefilm which may include, for example, a vacuum deposited aluminum layer,an adhesion promoting layer, a polyolefin or a microvoided polyolefinfilm, and a treated surface layer.

As hereinabove described, a biaxially oriented polymeric sheet may beused in the opaque support, either in the image-background layers or inthe barrier sheet, as a substrate for a metal coating. Microvoidedbiaxially oriented composite sheets are preferred and are convenientlymanufactured by coextrusion of the core and surface layers, followed bybiaxial orientation, whereby voids are formed around void-initiatingmaterial contained in the core layer. Such composite sheets aredisclosed in, for example, U.S. Pat. Nos. 4,377,616; 4,758,462; and4,632,869, the disclosures of which are hereby incorporated by referencein their entirety.

The core of the preferred composite sheet should be from 15 to 95% ofthe total thickness of the sheet, preferably from 30 to 85% of the totalthickness. The non-voided skins should thus total from 5 to 85% of thesheet, preferably from 15 to 70% of the thickness. Suitable classes ofthermoplastic polymers for the biaxially oriented sheet includepolyolefins, polyesters, polyamides, polycarbonates, cellulosic esters,polystyrene, polyvinyl resins, polysulfonamides, polyethers, polyimides,polyvinylidene fluoride, polyurethanes, polyphenylenesulfides,polytetrafluoroethylene, polyacetals, polysulfonates, polyesterionomers, and polyolefin ionomers. Copolymers and/or mixtures of thesepolymers can be used.

For the biaxially oriented sheet on the face side toward the imagingcomposition, preferred classes of thermoplastic polymers for thebiaxially oriented sheet and the core matrix polymer of the preferredcomposite sheet comprise polyolefins. Suitable polyolefins includepolypropylene, polyethylene, polymethylpentene, polystyrene,polybutylene and mixtures thereof. Polyolefin copolymers, includingcopolymers of propylene and ethylene such as hexene, butene, and octeneare also useful. Polypropylene is preferred, as it is low in cost, hasdesirable strength properties and is low in water vapor transmission.

The nonvoided skin layers of the composite sheet can be made of the samepolymeric materials as for the core matrix. The composite sheet can bemade with skin(s) of the same polymeric material as the core matrix, orit can be made with skin(s) of different polymeric composition than thecore matrix. For compatibility, an auxiliary layer can be used topromote adhesion of the skin layer to the core.

Addenda may be added to the core matrix and/or to the skins to improvethe whiteness of these sheets. This would include any process which isknown in the art including adding a white pigment, such as titaniumdioxide, barium sulfate, clay, or calcium carbonate. This would alsoinclude adding fluorescing agents which absorb energy in the UV regionand emit light largely in the blue region, or other additives whichwould improve the physical properties of the sheet or themanufacturability of the sheet.

Referring now to the top transparent support, it may also, optionallybut preferably, contain at least one layer that is a barrier material.This barrier material must have a preselected combination of properties,including thickness (if too thick, too hazy, if too thin not sufficientsupport) and optical properties. The barrier material must be highlytransparent, colorless, practical and cost effective, manufacturable orcommercially available, able to be applied via coating or lamination,and stable (non-yellowing). This combination of properties is difficultto find in a single material. Many materials previously used in formingbarriers in packaging do not meet all the necessary criteria alone or atall, for example, nylon, PC, PET, polyolefins, and saran polymers. Thelatter materials do not provide sufficient barrier properties unlessusing thick layers that are impractical in the present invention. Somematerials, while having good moisture barrier properties, have anunacceptable tint, for example silicon oxide coated polyester films.Some materials with exceptional moisture barrier properties are nottransparent, for example, aluminum metallized film or paper.

Thus, the assembly may comprise a first transparent support that is 5 to250 microns in thickness and has a light transmission of at least about80% at a wavelength of 550 nm and a water vapor transmission rate ofless than 0.77 g/m2/day (0.05 g/100 in²/day).

In yet another embodiment of the present invention, a self-containedphotohardenable imaging assembly further comprises an intermediate layercomprising a relatively resilient material (compared to firsttransparent support), wherein the Young's modulus of the resilientmaterial is 0.02 to 10 ksi. This has been found beneficial for betterdistributing the pressure applied to the microcapsules duringdevelopment.

Materials which can be used as a barrier sheet for a transparent supportinclude, but are not limited to, fluorinated polymers, ceramic coatedpolymers, for example aluminum oxide, indium tin oxide, or siliconnitride coated on polyester or other transparent polymeric substrates,and other sheet materials meeting the above limitations. Especiallypreferred are Al₂O₃ vacuum deposited coatings on a polyester film (forexample, Toppan™ GL-AE, available from Toppan Printing Co.) andchlorotrifluoroethylene homopolymer and copolymer films (for example,ACLAR™ films available from Honeywell Corp.).

It is preferred that a barrier layer is on both sides of the imaginglayer in order to maintain the relative humidity within the assembly. Itis optional but preferred that the relative humidity within theassembly, and particularly within the at least one imaging layer, ismaintained at greater than 40%, preferably greater than 50%, by sealingthe front and back supports on the sides, after the imaging layer hasequilibrated to the desired relative humidity. When both the top andbottom supports are barrier supports, it is also preferred (butoptional) that the peripheral edges of the self-contained assembly aresealed, to prevent water vapor transmission through the side edges,although this is less a concern in view of the small surface areacompared to the front and back of the imaging assembly. The edges of thefilms can be heat sealed together or they can be sealed by any otherconventional technique.

FIG. 3 shows a first embodiment of a laminate structure for an imagingassembly according to the present invention in which the transparentsupport 19 has a polyester substrate coated with a barrier layer of aceramic material such as aluminum oxide, indium tin oxide or siliconnitride. In the embodiment of FIG. 3, a polyester substrate 20, whichhere happens to be 12 microns thick, is coated with an aluminum oxidebarrier layer 22. Aluminum oxide is a preferred barrier material for thetransparent support. Aluminum oxide is an electrical insulator and istransparent to visible light. It is a strong, hard material and resistsattack by most chemicals. The aluminum oxide barrier layer 22 can bedeposited on the polymeric film substrate by vacuum deposition includingchemical vapor deposition, electron beam evaporation, plasma-typesputtering process, ion assisted process such as ion plating, as well asothers well known to those skilled in the art of vacuum coating ordeposition. The aluminum oxide barrier layer 22 may be overcoated with aUV absorbing subbing layer 24. The transparent support 19 (includinglayers 20 through 24) forms the transparent side to the imaging layer26. On the opaque side is a white support 30 with an aluminum barrierlayer 32 attached to the imaging layer 26 by an adhesive layer 28.

FIG. 4 shows a cross-sectional view of an opaque support for use in animaging assembly according to the present invention Starting with theside of the support that is nearest to the imaging composition, theopaque support comprises clear polyolefin layer 36, TiO₂ filledpolypropylene layer 38, microvoided polypropylene layer 40, TiO₂ filledpolypropylene layer 42, clear polyolefin layer 44, TiO₂ filledpolyolefin tie layer 46, paper sheet 48, polyolefin tie layer 50,aluminum metallized barrier sheet 52, and backing layer 54.

Adhesive materials useful for adhering the second support to theemulsion or imaging layer can be selected from the general class of“modified acrylics” that have good adhesion, which may be formulatedwith improved “tack” by addition of tackifying resins or other chemicaladditives. A useful adhesive must be designed for high initial adhesionand for adhesion to plastic substrates like polyester. It must have theability to flow quickly for laminating to porous material (the imaginglayer) and yet be inert with respect to the imaging layer. High strengthadhesives useful in this invention, for example, are the film labelstock adhesives of the 3M Company; including 3M's #300 and #310 adhesiveformulas which exhibit “inertness” to the imaging layer. Other examplesof adhesives useful in this invention are aqueous-based adhesives suchas Aeroset™ 2177 or Aeroset™t 2550, 3240, and 3250 which arecommercially available from Ashland Chemical Co., PD 0681, AP 6903, andW 3320 available from H. B. Fuller, or solvent-based pressure sensitiveadhesives such as PS 508 sold by Ashland Chemical Co. The adhesives maybe used separately or in combination. Preferably, the adhesive istransparent or translucent and most preferably it is a transparentadhesive which remains transparent even after subjecting the assembly toactinic radiation and pressure necessary to image-wise expose andrupture the microcapsules. The amount of the adhesive will varydepending on the nature of the adhesive and the support. The adhesive isgenerally applied in an amount of about 0.5 to 20 g/m².

A subbing layer for promoting adhesion between the transparent supportand the imaging layer must have good compatibility with the imaginglayer, must be transparent, must not effect the sensitometric responseof the imaging layer, and must be chemically stable. Amorphouspolyesters, which may be applied as an aqueous dispersion, have beenfound to work well as the subbing layer material. Polymers withmolecular weights of 5,000-15,000, with a low hydroxyl number and lowacid number, can be employed, for example, the AQ polymers from EastmanChemical Co. and, more particularly, AQ38 and AQ55. The subbing layer iscoated onto the transparent support at a dried coating weight of fromabout 0.1 to about 5.0 g/m², with a preferred dried coating weight offrom about 0.5 to 2.0 g/m².

Preferably the subbing layer also includes an ultraviolet (UV) rayabsorber. Many types of UV absorbing materials have been described inthe prior art, including U.S. Pat. Nos. 3,215,530, 3,707,375, 3,705,805,3,352,681, 3,278,448, 3,253,921, 3,738,837, 4,045,229, 4,790,959,4,853,471, 4,865,957, and 4,752,298, 5,977,219, 5,538,840 and UnitedKingdom Pat. 1,338,265. Most preferred UV absorbers are polymeric UVabsorbers prepared by the method described in U.S. Pat. Nos. 4,496,650,4,431,726, 4,464,462 and 4,645,735, 5,620,838, EP 0 190 003, U.S. Pat.Nos. 3,761,272, 3,813,255, 4,431,726, 4,455,368, and 4,645,735.

Suitable photohardenable compositions, photoinitiators, chromogenicmaterials, carrier oils and encapsulation techniques for the layer ofmicrocapsules are disclosed in U.S. Pat. No. 4,440,846, 4,772,541; and5,230,982. Although the latter photohardenable compositions arenon-silver systems, silver-based photohardenable microencapsulatedsystem such as that described in U.S. Pat. Nos. 4,912,011; 5,091,280 and5,118,590 and other patents assigned to Fuji Photo Film Co are alsosuitable for use in the present invention.

In accordance with the preferred embodiments of the invention, a fullcolor imaging system is provided in which the microcapsules aresensitive to red, green, and blue light, respectively. Thephotohardenable composition in at least one and preferably all threesets of microcapsules may be sensitized by a cationic dye-borate anioncomplex, e.g., a cyanine dye/borate complex as described in U.S. Pat.No. 4,772,541. For optimum color balance, the microcapsules aresensitive (lambda max) at about 450 nm, 540 nm, and 650 mn,respectively. Such a system is useful with visible light sources indirect transmission or reflection imaging. Such a material is useful inmaking contact prints or projected prints of color photographic slides.They are also useful in electronic imaging using lasers, light emittingdiodes, liquid crystal displays or pencil light sources of appropriatewavelengths.

Because cationic dye-borate anion complexes absorb at wavelengthsgreater than 400 nm, they are colored. The unreacted dye complex presentin the microcapsules in the low density image areas can cause undesiredcoloration in the background area of the final picture, for example, themixture of microcapsules tends to be green which may give the lowdensity image areas a slight greenish tint. Approaches to reducingundesired coloration in the low density image area as well as thedeveloped image include reducing the amount of photoinitiator used,adjusting the relative amounts of cyan, magenta and yellowmicrocapsules, or providing a compensating tint in the white opaquesupport.

The photohardenable compositions used in the microcapsules may alsocontain a disulfide coinitiator. Examples of useful disulfides aredescribed in U.S. Pat. No. 5,230,982. By means of the optional use ofsuch disulfides, the amount of the photoinitiators used in themicrocapsules can be reduced to levels such that the backgroundcoloration or residual stain is less than 0.3 and preferably less than0.25 density units.

The photohardenable compositions of the present invention can beencapsulated in various wall formers using conventional techniques,including coacervation, interfacial polymerization, polymerization ofone or more monomers in an oil, as well as various melting, dispersing,and cooling methods. To achieve maximum sensitivities, it is importantthat an encapsulation technique be used that provides high qualitycapsules which are responsive to changes in the internal phase viscosityin terms of their ability to rupture. Because the borate tends to beacid sensitive, encapsulation procedures conducted at higher pH (e.g.,greater than about 6) are preferred. Melamine-formaldehyde capsules areparticularly useful. U.S. Pat. No. 4,962,010 discloses a conventionalencapsulation useful in the present invention in which the microcapsulesare formed in the presence of pectin and sulfonated polystyrene assystem modifiers. A capsule size should be selected which minimizeslight attenuation. The mean diameter of the capsules used in thisinvention typically ranges from approximately 1 to 25 microns. As ageneral rule, image resolution improves as the capsule size decreases.Technically, however, the capsules can range in size from one or moremicrons up to the point where they become visible to the human eye.

The developer materials employed in carbonless paper technology areuseful in the present invention. Illustrative examples are clay mineralssuch as acid clay, active clay, attapulgite, etc.; organic acids such astannic acid, gallic acid, propyl gallate, etc.; acid polymers such asphenol-formaldehyde resins, phenol acetylene condensation resins,condensates between an organic carboxylic acid having at least onehydroxy group and formaldehyde, etc.; metal salts of aromatic carboxylicacids or derivatives thereof such as zinc salicylate, tin salicylate,zinc 2-hydroxy napththoate, zinc 3,5 di-tert butyl salicylate, zinc3,5-di-(a-methylbenzyl)salicylate, oil soluble metals salts orphenol-formaldehyde novolak resins (e.g., see U.S. Pat. Nos. 3,672,935and 3,732,120) such as zinc modified oil soluble phenol-formaldehyderesin as disclosed in U.S. Pat. No. 3,732,120, zinc carbonate etc. andmixtures thereof. The particle size of the developer material can affectthe quality of the image. In one embodiment, the developer particles areselected to be in the range of about 0.2 to 3 microns, preferably in therange of about 0.5 to 1.5 microns. One or more suitable binders selectedfrom polyethylene oxide, polyvinyl alcohol, polyacrylamide, acryliclatices, neoprene emulsions, polystyrene emulsions, and nitrileemulsions, etc. may be mixed with the developer and the microcapsules,typically in an amount of bout 1 to 8% by weight, to prepare a coatingcomposition. A preferred developer material is one which provides goodcompatibility with the microcapsule slurry solution, for exampleSchenectady International resin HRJ-4250 solution.

The self-contained imaging assembly used as photosensitive recordingmedium is not limited to the embodiments that have been describedbefore, but different variations or modifications thereof are possible.For example, instead of encapsulating the photocurable resin and thepolymerization initiator inside the microcapsules of the self-containedimaging assembly, the photocurable resin and the polymerizationinitiator can also be included in the material constituting themicrocapsules. Further, instead of photocurable microcapsules, theself-contained imaging assembly can contain photo-softeningmicrocapsules, for example, microcapsules which have sufficient strengthin the unexposed state, and which soften when exposed to light of apredetermined wavelength. In this case it is desirable to performthermal-curing by heat-fixing.

There is no need to use red, green and blue light to capture the imagein the imaging layer; depending on the characteristics of thephotosensitive recording medium, light with various wavelengths can beselected. For example, light emitting elements producing infrared light,red, and green, or light emitting elements producing far infrared light,near infrared light, and red can also be selected. Ultraviolet and farultraviolet are also advantageous examples of valid color choices forlight emitting elements. Moreover, the number of colors of the lightemitting elements is not limited to the three colors red, green, andblue; it is equally possible to use only one or two colors, or to selectfour colors, as in a typical color printer using yellow, magenta, cyan,and black, or even more colors. Furthermore, the choice of lightemitting elements includes, but is not limited to LEDs,electroluminescent lamps (EL), light emitting plasma and laser devices,and other light emitting elements.

The manufacture of an assembly according to the present invention isexemplified as follows. A clear support is sub-manufactured bylamination of three separate materials, a ceramic-coated first laminatedlayer, a polyester layer, and a second ceramic-coated second laminatedlayer. These three materials are formed into a clear support with theaddition of a UV absorbing subbing layer. At the same time an opaquesupport is sub-manufactured by lamination of three separate materials, apolyolefinic material, paper stock, and aluminum coated barrier sheet.These three materials are formed into an opaque support with theaddition of a backing/matte sheet.

An emulsion or image layer is then applied to the clear support to formthe first of two final components of the assembly, anemulsion-containing component which is then combined with the opaquesupport to form a final laminate which can be preconditioned to acertain relative humidity. The final laminate may then be cut and edgesealed, followed by packaging and bar coding.

In order to insure that the imaging system is effectively sealed betweenthe supports, a subbing layer is provided to attach the transparentsupports to the imaging layer and an adhesive is provided between theback support and the imaging layer. For optical clarity, the subbinglayer will typically be located between the first support and theimaging layer. However, which support receives the subbing layer andwhich support receives the adhesive is a function of which support iscoated with the wet imaging layer composition and which is assembledwith the coated and dried imaging layer. The support which is coatedwith the imaging layer composition (which is typically the frontsupport) will be provided with the subbing layer and the support whichis assembled will receive the adhesive. In accordance with the preferredembodiment of the invention, the subbing layer is formed from a compoundhaving chemical moieties such as hydroxy groups which will react withand bind to the microcapsules.

The imaging assembly of the present invention can be exposed in anysuitable camera or other exposure device to provide an image. Theimaging assembly of this invention is especially suitable for exposureusing a liquid crystal array or light emitting diodes driven by acomputer generated signal or a video signal for the reproduction ofimages from a video cassette recorder, a camcorder, or the like. It ispossible to utilize, for example, with the current state of technology,a very economical compact printer, weighing under 500 g and having asize less than 100,000 mm³ that prints directly from a digital camerautilizing a CompactFlash™ card interface and provides a resolution of150 ppi or more with continuous tone and over 250 gradation levels.

The print is “developed,” based on the “latent image” formed by theselectively photohardened microencapsulated color formers, by theapplication of pressure or by the application of both heat and pressure.See, for example, the image forming device described in U.S. Pat. No.5,884,114 to Iwasaki, in which a photo and pressure sensitive printerprovides the feeding and discharging of a photosensitive imaging mediumat the front of the printer housing, which device can have the addedadvantage of being easily integrated into other equipment such as apersonal computer. In this particular device, the latent image is formedby a movement in the main scanning direction of an LED-type exposurehead. Thereafter, an upper nip roller of a developing mechanism is movedfrom a separated position to a pressing position. The capsules that havenot been photohardened are ruptured by pressure and a full color imageis formed on the sheet, heat-fixing (which is optional to the presentinvention) is performed by a film heater, and the imaged assembly isdischarged from the front of the housing for the device or printer.

A typical pressure-type image-forming device (which can be referred toas a printer) typically comprises a printer housing with a lightproofcartridge for accommodating photosensitive imaging media (alternatelyreferred to as recording media) mounted to the front of the printerhousing so as to be easily detachable. In some devices, a preheater isemployed for preheating the photosensitive imaging medium. A typicalexposure mechanism may include an exposure head for exposing whilescanning in a direction perpendicular to the surface of the drawing anda developing mechanism for pressure development by means of a pair of anupper and a lower nip roller. The roller may be maintained underpressure by a spring. An optional fixing heater for heat-fixing thedeveloped photosensitive imaging medium may be used. A discharge traymay be provided at the rear end of the printer housing. The pressuresensitive printer may be designed so that sheets are both fed anddischarged at the front side of the printer housing.

An image forming device for treatment of the imaging media can, forexample, comprise exposure means for forming a latent image on theimaging medium upon exposure based on image information, developingmeans for developing the latent image by means of the coloring materialcoming out of the microcapsules when pressure is applied to thephotosensitive imaging medium on which the latent image was formed bythe exposure means, wherein the developing means comprise a pair of anupper and a lower nip roller facing each other and sandwiching thetransport path of the photosensitive imaging medium, pressing means forpressing one nip roller against the other nip roller, roller switchingmeans for alternately switching between a pressing position in which theone nip roller is brought into pressure contact with the other niproller and a separated position in which the one nip roller is separatedfrom the other nip roller, and a transport path for transporting thephotosensitive imaging medium comprises a feed path for feeding thephotosensitive imaging medium on the inlet side, a discharge path fordischarging the recorded photosensitive imaging medium.

In one embodiment, the developing mechanism may comprise a pair of anupper and a lower nip roller, a rectangular frame fixed inside theprinter housing for supporting the nip rollers, a pair of compressionsprings for pressing both ends of the roller axis of the upper niproller toward the lower nip roller, and a roller switching mechanism foralternately switching between a pressing position in which the upper niproller is brought into pressure contact with the lower nip roller and aseparated position in which it is separated from the lower nip roller.If the pressing force of each of the springs is 150 kgf, the upper niproller presses with a total force of 300 kgf on the lower nip roller.However, other means for applying pressure can be employed, for example,a pressure stylus.

A control unit for the image-forming device may comprise a CPU, a ROMand a RAM, an I/O interface, and drive circuits, wherein a steppingmotor for paper transport, a solenoid actuator for driving a switchingplate, a film heater, a motor for roller switching, a stepping motor fordriving the carriage, the exposure head, etc., are respectivelyconnected to the drive circuits. A connector and a control panel mayalso be connected to the control unit. In one embodiment, image data(RGB image data) from an external host computer may be fed via aconnector to the control unit.

The ROM can store control programs for controlling all operations of theprinter, a control program for calculating, from the input image data,the duration for which each LED of the exposure head is turned on andthe timing thereof, a control program for controlling the transport ofthe self-contained imaging assembly by controlling the stepping motorfor sheet transport synchronously with the exposure to green, red andblue light, a control program for controlling the scanning of theexposure head by controlling the stepping motor for driving the carriagesynchronously with the exposure to green, red and blue light, etc. Thedifferent buffers and memory types necessary for running the controlprograms are in the RAM. The number of copies to be printed, theenlargement or reduction ratio of the image, the size of the imageforming area of the imaging assembly, etc., input by an operator at thecontrol panel, can be stored in the memory of the RAM. Exposure can takeplace upon calculation of the driving conditions for the stepping motor.

In one type of image-forming device, when image data of an image is sentto the control unit, the image data is divided into R image data, Gimage data, and B image data and stored in a buffer of the RAM. Each LEDof an exposure heat can be electrically driven by a drive circuit via acable.

In one embodiment of practicing the invention, imaging medium sheets maybe packaged as a stack of sheets which go into the printer. Theindividual sheets may be picked from the stack of sheets and transportedinto the “printing path” of the printer. However, if two or more sheetsat the same time are picked up and fed into the printing path theprinter, the printer may become jammed, requiring disassembly by theuser. To avoid this problem, the static in the sheets may be reduced oreliminated just prior to the final packaging; and a precision hinge onthe printer film cassette or tray may be used. Also, a method to furtheraid the feeding of sheets into the printer is to add a “back coat” orbacking layer to the imaging medium. This is preferably coated on theouter surface of the bottom or second support (which has the adhesive onthe opposite side), typically the white support layer. This backinglayer material may be formulated to have some perceived aesthetic value(such as a writable or printable coating), but must have some differencerelative to the adjacent next sheet surface which causes these surfacesnot to adhere together. The preferred backing layer material has aslight roughness to aid the “printer pickup roller” initiating the sheetmovement into the printer, for example, a Sheffield Smoothness of150-180 Sheffield units, such as a standard face matte coating on 3Mlabel stock material. Other commercially available or known mattecoatings can also be used. In general, these coatings may include abinder and a grit or abrasive such as silica. Preferably, the front sideof the first support and the back side of the second support has acoefficient of friction of less than 0.4. For example, the backing layercan comprise a polyurethane (Zeneca Resins Neorez R9621® aqueousdispersed polyurethane) and a mixture of poly(divinyl benzene) mattebeads having a diameter of 6 and 14 microns. A wide variety of binderscould be used effectively in the backing layer including polyurethanes,polyesters, polymers containing ethylenically unsaturated monomersincluding styrene and its derivatives, (meth)acrylic acid and theirderivatives, divinyl benzene, (meth)acrylamide polymers, hydrophiliccolloids including gelatin, cellulose esters, etc.

The present invention is illustrated in more detail by the followingnon-limiting example.

EXAMPLE 1

The following opaque supports for use in the present invention wereprepared by extrusion laminating a biaxially oriented opaque sheet tothe face side of a photographic grade cellullose paper and an aluminummetallized composite film to the back side of the paper.

Face side of Opaque Support

A biaxially oriented multi-layer sheet of polypropylene having a totalthickness of 30 microns and containing in order, a polyethylene skinlayer, a TiO₂ containing layer having approximately 15% TiO₂, acavitated polypropylene core, and a layer of clear polypropylene, wasextrusion laminated to a 75 micron thick photographic grade celluloseraw stock paper using a tie layer of low density polyethylene with adensity of 0.923 g/cm³ and a melt index of 4.2 at 12 g/m² to adhere theoriented sheet to the paper base.

Back side of Opaque Support

The following metallized composite films were laminated to the back sideof the 75 micron thick photographic grade cellulose raw stock paperusing a tie layer of ethylene-methyl acrylate copolymer resin having adensity of 0.94 g/cm³ and a melt index of 2.0 at 12 g/m² in order toprepare opaque laminated supports of the invention. The metallized sideof the composite films was laminated facing the paper base.

Opaque Support A was a 205MET TWSB™ composite film from Exxon-MobilCorporation having a thickness of about 50 micron and having an aluminummetallized layer on one side of the composite film, a treated clearlayer on the other side, and a cavitated white core layer. A thinadhesion promoting layer was present between the vacuum depositedaluminum metallized layer and the core layer. The opaque support A thusformed had a total thickness of about 175 microns and a water vaportransmission rate of about 0.047 g/m²/day (0.003 g/100 in²/day) asmeasured according to the procedures set forth in ASTM F1249 at 38° C.and 100% relative humidity.

Opaque Support B was a Bicor 70 MET-HB™ from Exxon-Mobil Corporationhaving a thickness of about 17.5 microns and having an aluminummetallized layer on one side of the composite film, a sealant layer onthe other side, a high energy treated layer interfacing with themetallized aluminum layer and a polypropylene core layer. To reduce themetallic color, the support was further laminated on the surface of thesealant layer with 350 TWL K18™ from Exxon-Mobil Corporation which has athickness of about 35 microns and consisted of a cavitated core layerand two layers each containing about 18% TiO₂ by weight using a tielayer of a ethylene-methyl acrylate copolymer resin. The opaque supportB thus formed has a total thickness of about 182.5 microns and a watervapor transmission rate of about 0.063 g/m²/day (0.004 g/100 in²/day) asmeasured according to the procedures set forth in ASTM F1249 at 38° C.and 100% relative humidity.

Opaque Support C was 35MU842™ from Exxon-Mobil Corporation having athickness of about 35 microns and having an aluminum metallized layer onone side of the composite film, a treated clear layer on the other side,and a cavitated white core layer. A thin adhesion promoting layer waspresent between the vacuum deposited aluminum metallized layer and thecore layer. The opaque support C thus formed had a thickness of about167.5 microns and a water vapor transmission rate of about 0.063 to0.154 g/m²/day (0.004 to 0.01 g/100 in²/day) as measured according tothe procedures set forth in ASTM F1249 at 38° C. and 100% relativehumidity.

EXAMPLE 2

This example illustrates the effect of a moisture barrier such as theopaque supports described in Example 1 on the sensitometric response ofan imaging assembly containing photohardenable microcapsules. Imagingmedia containing photohardenable microcapsules in an imaging layer,commercially available from Cycolor, Inc, were obtained packaged in aplastic cartridge. The media in the cartridge were preconditioned at 80%relative humidity/70° F. for 3 days. Prints were then made with some ofthese preconditioned media using a Vivitar VPP-150™ Photo Printer. Theseprints provided the sensitometric response for fresh media. Theremaining preconditioned media were then removed from the cartridge andseparated in a darkroom into two groups, Group I and Group II.Individual samples of media in group I were packaged in separate bagsmade of a barrier material having a water vapor transmission rate ofabout 0.47 g/m²/day (0.03 g/100 in²/day) in a darkroom at 80% relativehumidity. The bag was made to essentially the same dimensions (lengthtimes width) as the media and was sealed on the edges by heat. The mediain Group II were used as the control. Both groups of media were thenkept in a darkroom at 40% relative humidity/70° F. and prints were madewith a Vivitar VPP-150™ Photo Printer at given time intervals, 0, 2, 4,7, 14, 28, 35, 42 and 49 days, to determine the effect of the lowerhumidity on sensitometric response for the two groups of media. TheGroup I media were removed from the sealed bag just prior to printing.The Group I media were removed from the sealed bag and loaded into anempty cartridge just prior to printing. The respective optical densities(Dmin) of prints from both groups were measured using an X-Rite 820TR™Densitometer in order to obtain Dmin values for the cyan dye, magentadye, and yellow dye, respectively. The results thereof are shown inFIGS. 8 to 10.

FIG. 5 shows the Dmin for the yellow dye for prints made from media fromGroup I and Group II (control) that were exposed to 40% relativehumidity for various times.

FIG. 6 shows the Dmin for the magenta dye for prints made from mediafrom Group I and Group II (control) that were exposed to 40% relativehumidity for various times.

FIG. 7 shows the Dmin for the cyan dye for prints made from media fromGroup I and Group II (control) that were exposed to 40% relativehumidity for various times.

These experiments show that the Dmin for the control (Group II media)increased significantly after only 2 days. On the other hand, the GroupI media that had a moisture barrier showed no change in Dmin afterexposure to 40% relative humidity for as much as 35 days. The results ofthis study demonstrate that laminating the media with a barrier materialaccording to the present invention would minimize variations insensitometric response of the imaging assembly due to changes inhumidity.

Having described the invention in detail and by reference to preferredembodiments thereof it will be apparent that modifications andvariations are possible without departing from the scope of theinvention defined in the appended claims.

What is claimed is:
 1. A self-contained photohardenable imaging assemblycomprising in order from front to back the following: a transparentfirst support that is 10 to 250 microns in thickness and has a lighttransmission of at least about 80% at a wavelength at 550 nm; at leastone imaging layer comprising a plurality of photohardenablemicrocapsules encapsulating a color precursor which can react with adeveloper material in the same or an adjacent imaging layer; an opaquesecond support that is 10 to 250 microns thick and has a water vaportransmission rate of less than 0.77 g/m2/day (0.05 g/100 in²/day) and alight reflectance of greater than 80%, said second support comprising,also in order, one or more image-background layers comprising aneffective amount of a white pigment for producing photographic qualitywhiteness in front of a metallic barrier layer.
 2. The imaging assemblyof claim 1, wherein the metallic barrier layer comprises a metal foil.3. The imaging assembly of claim 1, wherein the metallic barrier layeris coated on a plastic film.
 4. The imaging assembly of claim 1, whereinthe image-background layers comprise a microvoided polymer layer.
 5. Theimaging assembly of claim 1, wherein the image-background layerscomprise a polyolefinic sheet overlying cellulosic paper or microvoidedor non-microvoided polyester.
 6. The imaging assembly of claim 4,wherein the microvoided polymer layer is a microvoided polyester.
 7. Theimaging assembly of claim 4, wherein the microvoided polymer layer is abiaxially oriented microvoided polyolefin.
 8. The imaging assembly ofclaim 1, wherein the metallic barrier layer comprises aluminum metal. 9.The imaging assembly of claim 7, wherein the polyolefin ispolypropylene.
 10. The imaging assembly of claim 1, wherein the metallicbarrier layer comprises part of a sheet that is laminated or coated witha pigmented layer to substantially reduce the metallic color of themetallic barrier layer when viewing the imaging assembly from the back.11. The imaging assembly of claim 1, wherein the barrier sheet has anWVTR value of less than 0.77 g/m2/day (0.05 g/100 in²/day) per 25 micronof thickness.
 12. The imaging assembly of claim 1, wherein an adhesivelayer is disposed between said second support and said at least oneimaging layer.
 13. The imaging assembly of claim 1, wherein the frontside of the transparent support and the back side of the opaque supporthas a coefficient of friction of less than 0.4.
 14. The imaging assemblyof claim 1, wherein the imaging assembly is sealed between thetransparent support and the opaque support.
 15. The imaging assembly ofclaim 1, wherein said transparent support comprises a barrier layerselected from the group consisting of fluorinated polymers, inorganicoxides, and inorganic nitrides.
 16. The imaging assembly of claim 1,wherein said pigment is titanium dioxide.
 17. The imaging assembly ofclaim 1, wherein said microcapsules are melamine-formaldehydemicrocapsules and said developer is a phenolic resin.
 18. A sealedself-contained photohardenable imaging assembly comprising in order fromfront to back: a first transparent support that is 10 to 250 microns inthickness and has a light transmission of at least about 80% at awavelength of 450 to 800 nm and a water vapor transmission rate of lessthan 0.77 g/m²/day (0.05 g/100 in²/day); one or more imaging layerscomprising a plurality of photohardenable microcapsules encapsulating acolor precursor which can react with a developer material in the same oran adjacent imaging layer; a second support which is opaque, 10 to 250microns thick, having a water vapor transmission rate of less than 0.77g/m²/day (0.05 g/100 in²/day), said second support comprising in orderstarting from the outside of the assembly: a metallic barrier layer; oneor more image-background layers comprising a polyolefin sheet overlyinga paper and/or polyester material having a thickness of 10 to 250microns and an effective amount of a white pigment for producingphotographic quality whiteness in front of the metallic barrier layer;wherein the opaque support has a reflection value of greater than 90% atits front side.
 19. The imaging assembly of claim 18, wherein theimage-background layers comprises a biaxially oriented microvoidedpolyolefin.
 20. The imaging assembly of claim 19, wherein said biaxiallyoriented sheet microvoided polyolefin comprises polypropylene.
 21. Theimaging assembly of claim 18, wherein the metallic barrier layer islaminated or coated with a pigmented layer to reduce the metallic colorof the barrier layer when viewed from the outside of the imagingassembly.
 22. The imaging assembly of claim 18, wherein the front of theimage-background layers have a light reflectance of greater than 95%.23. The imaging assembly of claim 18, wherein the metallic barrier layerhas WVTR value of less than 0.77 g/m2/day (0.05 g/100 in²/day) per 25micron of thickness.
 24. The imaging assembly of claim 18, wherein saidimage-background layers comprise, from front to back, a polyolefiniclayer and a cellulose fiber paper layer.
 25. A self-containedphotohardenable imaging assembly comprising in order from front to backthe following: a transparent first support that is 10 to 250 microns inthickness and has a light transmission of at least about 80% at awavelength at 550 nm, which transparent support comprises a barrierlayer selected from the group consisting of fluorinated polymers,inorganic oxides, and inorganic nitrides; at least one imaging layercomprising a plurality of photohardenable microcapsules encapsulating acolor precursor which can react with a developer material in the same oran adjacent imaging layer; an opaque second support that is 10 to 250microns thick and has a water vapor transmission rate of less than 0.77g/m2/day (0.05 g/100 in²/day) and a light reflectance of greater than80%, said second support comprising, also in order, one or moreimage-background layers comprising an effective amount of a whitepigment for producing photographic quality whiteness in front of ametallic barrier layer.